xml2po – and some usage tips. Can either work with XHTML, DocBook, or your own custom written XML format. An XSLT can be used to generate the post-translation XHTML. (Thanks Goran Rakic!)

The new gnu.org translation system: GNUnited Nations. They say it currently can only work for gnu.org’s layout, but I guess a bit of hacking could make it work with other sites. The 0.1 release announcement has a little bit of other info.

Plus, although not based on gettext, the build system of fsfeurope.org is another way of managing translations. Most of the work is done by build.pl.